The invention relates to a plasma display panel as defined in the precharacterizing part of claim 1, and more specifically to the electrode structure thereof. The invention also relates to a method of driving a plasma display panel as defined in the precharacterizing part of claim 13.
The invention applies to an AC plasma display panel of the surface discharge type.
Plasma display panels and methods of driving same are known in the art. Plasma display panels are matrix devices comprising individual cells defined by the intersection of rows and columns. The structure of a panel 1 known from EP 0 762 373 is shown schematically in FIG. 1 in a front view. FIGS. 2a and 2b are a detailed perspective and a side view, respectively, of a single cell 2. The panel comprises a front plate 3 made of transparent material and a back plate 4. A first set of parallel address electrodes 5 a1, a2, a3, . . . an . . . are located in a vertical direction on the back plate. Barrier ribs 6, located parallel to the address electrodes 5, also on the back plate 4, perform the function of separating cells 2 from neighbouring columns. A second set of electrodes comprises common electrodes 7 and scan electrodes 8. These electrodes are located on a front plate 3, facing the address electrodes 5 on the back plate 4. The common electrodes 7 are divided into two groups, c1 and c2. The scan electrodes 8 s1, s2, s3 . . . are separately addressable. Said second set of electrodes is oriented in a horizontal direction, substantially orthogonal to the address electrodes 5. Phosphors 9 deposited on the back plate 4 perform the function of converting the ultraviolet light UV produced by a gas discharge GD between a common electrode 7 and a scan electrode 8 into visible light VL. By selecting different types of phosphors 9, one produces light of the desired colour, e.g. red, green, blue.
Common and scan electrodes known in the art may be formed of a metallic part 10 and a transparent part 11. The metallic part 10 ensures the conduction of the current flowing through the electrode. The transparent part 11 extends the voltages applied to the electrode across the desired areas of the cells 2. The transparent parts 11 may be made of a thin layer of metal oxides (ITO).
When displaying successive picture frames on such a plasma display panel 1, a frame is divided into an odd field and a subsequent, even field. Odd rows, i.e. rows between electrodes c1 and s1, c2 and s2, c1 and s3 in FIG. 1, produce light during an odd field, and even rows, i.e. rows between electrodes s1 and c2, s2 and c1 in FIG. 1, produce light during an even field. A drawback of this (interlacing) method is that alternation of the odd and even fields causes line flicker and a reduction of image quality. The driving scheme requires the common electrodes to be grouped in two interleaved sets, the c1 common electrodes and the c2 common electrodes.
In known plasma display panels, each column requires one address electrode. A VGA display, with 640 columns, requires 1920 address electrodes (one for each colour). Increasing the picture resolution by adding columns further increases the number of address electrodes and therefore the cost of the panel and the associated driving electronics.
It is an object of the invention to provide a plasma display panel with a reduced number of electrodes. It is also an object of the invention to provide a method of driving a plasma display panel according to the invention, having a good image quality.
The invention provides a plasma display panel as defined in claim 1, in which an address electrode extends over more than one column, covering at least a part of a cell in a first column in one row, and at least a part of a cell in another column in the row immediately below, no other address electrode extending over the cell immediately below the first cell, nor over the cell immediately above the second cell. The amount of address electrodes is thereby reduced by half with respect to a plasma display panel of the known type. The plasma display panel appears as a checkerboard, where one cell out of every two cells is addressable.
In a preferred embodiment as defined in claim 2, the common and scan electrodes comprise a metal part and a set of transparent parts. These transparent parts are formed in such a way as to allow discharges in one out of every two cells of the panel, in a checkerboard fashion.
The transparent parts may be made of areas of a thin layer of metal oxide (ITO). In a preferred embodiment as defined in claim 3, the common and scan electrodes have transparent parts made of areas of a thin metal grid. This has the advantage that the production of the metallic part and the transparent parts of an electrode may by performed in a single process step.
The address electrodes defined in claim 4, formed as straight strips underneath one out of every two barrier ribs, are especially easy to produce, and are robust. The layout of the transparent parts in a checkerboard fashion ensures that only the desired cells produce light.
The zigzag address electrodes defined in claim 5 may reach cells in adjacent columns in each successive row, while remaining thin. Thin electrodes have the advantage of a reduced capacity and therefore require less power. The period of the zigzag electrodes may encompass two or more rows. The address electrodes defined in claim 5 may even be formed in diagonals across the whole height of the panel. Zigzag electrodes defined in claim 5 have the additional advantage that they only cover cells where a discharge is desired, thereby reducing the risk of spurious discharges.
As claimed in claim the transparent parts of common and scan electrodes may, 6, extend slightly over the cell immediately above, or below, in the same column. The discharge space is thereby extended further in the vertical direction. This increases the part of the surface of the panel that produces light, and thereby increases the brightness.
As defined in claim 7, the transparent parts may extend over only part of the width of a cell. The capacity of the electrodes is thereby reduced, and the currents required to drive the panel are reduced accordingly. As defined in claim 8, the transparent parts may have a wider portion near said gap. This improves the quality of a discharge occurring between said pair of transparent parts.
As defined in claim 9, the said two transparent parts may, extend side by side, the gap between said two transparent parts extending vertically over said cell. The surface gas discharge between said two transparent parts occurs over an increased gap length and is thereby improved.
As defined in claim 10, the address electrodes may, comprise an extension extending substantially over the gap. This extension increases the coverage of the address electrodes to the desired cells. These extensions may be applied to the straight address electrodes defined in claim 4 as well as to the zigzag address electrodes of claim 5.
In a preferred embodiment as defined in claim 11, the barrier ribs have a shape forming enlarged cells where these are used for producing light, and cells of reduced width where these remain unlit. The ratio of light producing area to unlit area is thereby increased, and the brightness of the panel is significantly improved. Address electrodes in this embodiment may be of the straight type or of the zigzag type. The cells of reduced width may be reduced to nil or nearly nil area.
In the embodiment defined in claim 11, the transparent parts of the common and scan electrodes may be formed as continuous strips as defined in claim 12. The production cost of the panel is thereby reduced. No precise alignment in the horizontal direction of the front plate with respect to the back plate is necessary.
The invention also provides a method of driving a plasma display panel according to the invention, comprising the steps of
(a) performing a whole-screen write discharge and self-erasing discharge;
(b) performing an addressing of all rows of the panel by applying negative pulses to odd scan electrodes S1,S3, . . . and simultaneously positive pulses to common electrodes C1, and negative pulses to even scan electrodes S2,S4 . . . and simultaneously positive pulses to common electrodes C2, for selecting odd rows, by applying negative pulses to odd scan electrodes S1,S3, . . . and simultaneously positive pulses to common electrodes C2, and negative pulses to even scan electrodes S2,S4 . . . and simultaneously positive pulses to common electrodes C1, for selecting even rows, and by applying a positive pulse to the address electrodes of the columns where a cell is to be lit in the selected row, thereby priming the cells to be lit;
(c) performing a sustain discharge in all cells of the panel that have been primed in the addressing step by supplying positive pulses to all common electrodes C1, C2, and, in counterphase thereto, positive pulses to all scan electrodes S1,S2, . . . Sn.
Step a can be done, for example, by applying voltage pulses to common electrodes C1 and C2 and to address electrodes A1 . . . An
During the address phase, the rows of the panel may be addressed in any order, provided that all rows are eventually addressed. The driving method according to the invention has the advantage that, during the sustain phase, all rows of the panel are simultaneously driven, whereas in the prior art, odd rows are driven during the odd fields, and even rows are driven during the even fields. An advantage of the present invention is that line flicker due to interlacing is avoided and the image quality is correspondingly improved.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.